1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus.
2. Description of the Related Art
Recently proposed photoelectric conversion apparatuses include optical waveguides and in-layer lenses so as to increase the quantity of light to be incident on photoelectric conversion portions.
FIG. 8 of Japanese Patent Laid-Open No. 2007-201091 illustrates the following solid-state image pickup element as a photoelectric conversion apparatus. A planarizing layer having a through hole is provided on a semiconductor substrate having a photoelectric conversion portion. A first highly refractive material is provided over the planarizing layer such that the through hole is filled with the first highly refractive material, which forms an optical waveguide. An inner lens, as an in-layer lens, made of a second highly refractive material is provided on the first highly refractive material. A top microlens is provided on the inner lens.
FIG. 1 of Japanese Patent Laid-Open No. 2008-192951 illustrates the following solid-state image pickup apparatus as a photoelectric conversion apparatus. A plurality of interlayer dielectric films are stacked on a semiconductor substrate having photoelectric conversion elements. Openings are provided in portions of the stack of interlayer dielectric films in such a manner as to overlap the respective photoelectric conversion elements. Optical waveguides are embedded in the respective openings. In-layer lenses are provided on the respective optical waveguides. Top lenses are provided on the respective in-layer lenses.
In a photoelectric conversion apparatus to which the solid-state image pickup element disclosed by Japanese Patent Laid-Open No. 2007-201091 is applied, a film made of a highly refractive material that is the same as a material forming the in-layer lens is interposed between the in-layer lens and the optical waveguide. Therefore, some of light transmitted through the in-layer lens may not enter the optical waveguide. In the photoelectric conversion apparatus disclosed by Japanese Patent Laid-Open No. 2008-192951, each of the optical waveguides is in contact with a corresponding one of the in-layer lenses. In such a configuration, some of light incident on a peripheral region of the in-layer lens may not enter the optical waveguide.
The above situations are noticeable with light rays that are obliquely incident on the in-layer lens with respect to the optical axis. Therefore, in such a photoelectric conversion apparatus, there may be a difference in sensitivity between a group of pixels around the center of the image pickup area and a group of pixels near ends of the image pickup area. This is because pixels near ends of the image pickup area tend to receive more oblique light rays than pixels around the center of the image pickup area. This phenomenon becomes more noticeable as the image pickup area of the photoelectric conversion apparatus becomes larger.